Intracranial and peripheral aneurysms have conventionally been treated by percutaneous or endovascular implantation of vascular occlusive material such as devices, fluid or other materials that are placed in the aneurysms before rupture (or sometimes on rupture). For example, generally stated, endovascular treatment of brain or peripheral aneurysms can involve insertion of a catheter (small plastic tube) into the femoral artery in the patient's leg. The catheter is navigated through the vascular system, into the aneurysm. The desired material, device or liquid, is then implanted into the aneurysm.
Examples of implantable devices and materials include microcoils (spirals and framing coils) and/or liquid embolics. Two particular types of devices used to treat intracranial aneurysms are mechanical detachable spirals (MDS) and Guglielmi detachable coils (GDC). The liquid embolic materials are mainly polymeric biomaterials and are injected directly into the aneurysms sacs. An example of a liquid embolic is a cyanoacrylate liquid embolic agent.
The detachable implantable coils are used in procedures known as “aneurysm coiling” which has become a relatively routine clinical procedure. For the aneurysm coiling procedure, miniaturized platinum coils are threaded through the catheter and deployed into the aneurysm, blocking blood flow into the aneurysm and preventing rupture. The coils are made of platinum so that they can be visible via X-ray and are sufficiently flexible to conform to the aneurysm shape. The endovascular coiling, or filling, of the aneurysm is called “embolization” and can be performed under general anesthesia or light sedation. It is said that more than 125,000 patients worldwide have been treated with detachable platinum coils.
Notwithstanding the above, it is believed that in greater than about 15% of cases, aneurysms treated with implanted devices and/or materials may undergo recanalization leading to aneurysm recurrence. To monitor the potential risk of aneurysm recurrence and/or recanalization, patients with microcoils or other types of vascular occlusive treatment types may need relatively frequent follow-up evaluations. The follow-up evaluations typically employ digital subtraction angiography (DSA) taken at about 6 months post-implantation with subsequent MRI (Magnetic Resonance Imaging) being obtained at about every 6 months for several years, typically for about three to five years.
Unfortunately, the follow-up MRIs of patients with coiled intracranial aneurysms are often inadequate and have limited utility for diagnostic purposes. This limitation may be related to coil-generated artifacts that mimic residual flow within the coiled aneurismal cavity. CT imaging can suffer from image distortion secondary to beam hardening artifacts related to microcoils, and therefore, may provide little useful information about aneurysm recanalization. See, e.g., Masaryk et al., Utility of CT angiography and MR angiography for the follow-up of experimental aneurysms treated with stents or Guglielmi detachable coils, AJNR Am J Neuroradiol 2000; 21(8): 1523-1531. DSA remains the gold standard for follow-up diagnosis in patients with coiled-intracranial aneurysms. However, DSA is considered an invasive procedure and can carry a small but significant risk of neurological complications.
MRI is considered by some researchers to be the only noninvasive follow-up modality that may be used effectively for monitoring intracranial aneurysms. See, for example, Masaryk et al., cited above, and Saatci et al., CT and MR imaging findings and their implications in the follow-up of patients with intracranial aneurysms treated with endosaccular occlusion with onyx, AJNR AM J Neuroradiol 2003; 24 (4): 567-578.
Despite the foregoing, there remains a need to improve MRI data obtained for evaluation of patients with intracranial or peripheral aneurysms, particularly for those patients having implanted vascular occlusive materials and/or devices.